VULCANISM 



373 



canoes, while other and larger areas had few or none. This is not 

 equally true of all periods, as will be seen in the historical studies 

 that follow. There were periods when volcanic activity was wide- 

 spread and energetic, and other periods when it was limited in 

 amount and in distribution. The known facts do not indicate a 



ttavna Loa 



Fig. 292. Profile of the cone of Mauna Loa. Vertical scale same as hori- 

 zontal. (U. S. Geol. Surv.) 



steady decline in volcanic activity, but rather a periodicity; at 

 least this is so for the portion of the globe that is now known well 

 enough to warrant conclusions. One of the greatest of the vol- 

 canic periods falls within the Cenozoic era, just preceding the present 

 geological period, and the volcanic activity of the present is perhaps 

 but a declining phase of the activity of that time. 



Fig. 293. Cinder cone. 



